The Collaborative International Dictionary of English v.0.48:

Chlorination \Chlo`ri*na"tion\, n.
   The act or process of subjecting anything to the action of
   chlorine; especially, a process for the extraction of gold by
   exposure of the auriferous material to chlorine gas.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chlorination
    n 1: the addition or substitution of chlorine in organic
         compounds
    2: disinfection of water by the addition of small amounts of
       chlorine or a chlorine compound